Alkylaromatic compounds and particularly alkylaromatic hydrocarbons will find a wide variety of uses in the chemical field. For example, toluene, which may be obtained by the catalytic reforming of petroleum, by fractional distillation of coal tar light oil, by extraction from coal gas, etc., is used in aviation gasoline as well as high octane blending stock, as a solvent, in paints and coatings, rubber cement, in medicines, dyes, perfumes or as an intermediate in the preparation of polyurethane resins, explosives, detergents, etc. Likewise, the isomeric xylenes also find a wide variety of uses. For example, o-xylene may be used in vitamin and pharmaceutical syntheses, in dyes, insecticides, in the manufacture of phthalic anhydride; m-xylene may be used as a solvent, as an intermediate for dyes and organic syntheses; p-xylene is used in the synthesis of terephthalic acid which is an intermediate for the production of synthetic resins and fibers such as Dacron, Myler, etc., while mixtures of the isomeric xylenes may be used in aviation gasoline, protective coatings, as a solvent for alkyl resins, lacquers, enamels, rubber cements, etc. Other alkylaromatic hydrocarbons which are also useful in commercial chemical processes include cumene (isopropylbenzene) which is used as an additive to aviation gasoline or in the production of other chemicals such as phenol, acetone, etc., and ethylbenzene which is used as a solvent and diluent or as an intermediate in the production of styrene.
As hereinbefore set forth, the simple alkylaromatics such as toluene and the isomeric xylenes are obtained from petroleum or gas. However, these compounds may also be synthesized by treating an aromatic compound such as benzene or toluene with an alkylating agent comprising a synthesis gas which contains hydrogen and carbon monoxide and in some instances carbon dioxide. One such process is described in U.S. Pat. No. 4,487,984 in which the aromatic compound is reacted with a synthesis gas in the presence of a catalyst system which comprises a composite of oxides of copper, zinc and aluminum or chromium in conjunction with an aluminosilicate. However, as will hereinafter be shown in greater detail, we have now discovered that an aromatic compound may be alkylated utilizing, as the alkylating agent, a synthesis gas in which the catalyst which is employed to effect the alkylation reaction comprises a composite of oxides of only zinc and chromium along with an aluminosilicate. The utilization of the catalyst system of our invention as opposed to the catalyst system described in the aforementioned patent will permit the use of higher reaction temperatures inasmuch as our catalyst system will be more stable at higher temperatures due to the absence of the oxide of copper in the composite. This is due to the fact that the copper oxide which is present in the catalyst system of the prior patent will have a tendency to lose its activity at relatively high operating temperature, i.e. above about 280.degree. C. and thus render the catalyst system relatively inoperable. The ability to use higher operating pressures may be of an advantage in the event that higher temperatures, shorter space times may become commercially attractive to the operator of the reaction system. In addition, by utilizing only the oxides of zinc and chromium as one component of the catalyst system, it is also possible to utilize, as the aluminosilicate component of the system, a compound which does not require a relatively high silica-to-alumina content, thereby permitting the employment of other aluminosilicates which may be relatively less expensive, thereby lowering the cost of operation of the desired reaction.
In addition to the aforementioned U.S. patent, there are also other patents which describe catalyst compositions similar in nature to the composition employed in this process. However, the catalyst set forth in these references is utilized for various reactions other than an alkylation reaction. For example, U.S. Pat. No. 3,392,106 describes a hydrocracking process in which a catalyst comprising a crystalline aluminosilicate composite with a zinc compound and a compound of a metal of Group IV of the Periodic Table is used to treat a petroleum feedstock at hydrocracking conditions to convert said petroleum feedstock into components which are useful to increase the octane number of fuels such as gasoline. U.S. Pat. No. 4,180,516 discloses a catalyst comprising as a first component a carbon monoxide reduction catalyst such as a zinc-chromium mixture composited with a crystalline aluminosilicate zeolite to convert snythesis gas to aromatic hydrocarbons. In like manner, U.S. Pat. No. 3,699,181 discloses a catalyst comprising a Group VIB metal of the Periodic Table such as chromium, molybdenum or tungsten composited on a synthetic mordenite base to effect an alkyl transfer of alkylaromatics. An example of this process is subjecting toluene to the action of the catalyst to prepare benzene, toluene and isomeric xylenes. In a similar vein, U.S. Pat. No. 3,915,895 also discloses a catalyst for the disproportionation of alkylaromatic compounds such as toluene utilizing as a catalyst for this process a composite comprising hydrogen, mordenite and a Group IB metal such as copper or silver impregnated on the mordenite and also containing, if so desired, a Group VIB metal. U.S. Pat. No. 4,472,535 is drawn to a method for converting synthesis gas selectively to ethane utilizing a catalyst comprising a crystalline zeolite component in conjunction with a metal such as chromium, zinc or aluminum along with, if so desired, potassium. In addition to these U.S. patents, French Patent No.2538-266-A discloses a catalyst comprising two transition metals in association with a dealuminized active mordenite to produce for use in the conversion of synthesis gas to organic compounds containing a high ethylene content.
As was hereinbefore set forth, none of the aforementioned patents disclose an alkylation process wherein alkylaromatic compounds may be prepared in a one-step process by treating an aromatic compound with synthesis gas in the presence of a catalyst system of the type hereinafter set forth in greater detail.